1. Field of the Invention
The present invention relates to a method of cleaning semiconductor production equipment. More specifically, the present invention relates to a method of reducing the presence of halogens or halogen-containing compounds in an environment used for semiconductor device fabrication such as a deposition chamber.
2. State of the Art
Semiconductor devices are fabricated by depositing multiple layers of material onto a surface of a substrate, such as a silicon wafer or other bulk semiconductor substrate. The material layers are deposited by various techniques, such as chemical vapor deposition (CVD) or physical vapor deposition (PVD), with each material layer being formed sequentially in a deposition chamber. Many of the techniques used to deposit the material layers produce impurities or contaminants that accumulate on walls or other surfaces of the deposition chamber. For instance, the impurities form on exposed surfaces on the interior of the deposition chamber. If the impurities subsequently dislodge or desorb from these surfaces when a material layer is being deposited, the impurities are incorporated into that material layer and may cause structural and compositional flaws in the semiconductor device that is being formed. The impurities affect the properties of the material layer and compromise its function in the semiconductor device. To limit the number of defective semiconductor devices that are produced, the surfaces of the deposition chamber must be periodically cleaned to remove the impurities before the chamber is again used for material layer deposition.
Wet cleaning processes have typically been used to remove the impurities by cleaning the interior of a deposition chamber with a liquid cleaning agent. However, these processes are time consuming and labor intensive. Dry cleaning processes, which utilize gaseous cleaning agents, have also been used to clean deposition chambers. The gaseous cleaning agents typically include halogen or halogen-containing compounds, such as nitrogen trifluoride (NF3), sulfur hexafluoride (SF6), tetrafluoroethylene (C2F4), chlorine, and chlorine trifluoride (ClF3). For instance, NF3 is commonly used to clean deposition chambers after tungsten or silicon oxide layers have been deposited. Chlorine is used to remove impurities remaining after the deposition of titanium or titanium nitride layers. The gaseous cleaning agents are introduced into a deposition chamber, where they react with the impurities to form volatile compounds that include the impurities. The volatilized impurities are then exhausted from the deposition chamber.
While the gaseous cleaning agents may be used effectively to remove the impurities from a deposition chamber, the gaseous cleaning agents themselves are difficult to remove because they are reactive and adsorb to the surfaces thereof. In other words, the gaseous cleaning agents remain in the “clean” deposition chamber after the cleaning process. Therefore, when additional material layers are formed on a semiconductor substrate disposed within the deposition chamber after the cleaning process, the halogen-containing compounds desorb from the surfaces and are incorporated into the material layers. Halogen-containing compounds are also produced by the reaction of the gaseous cleaning agents with post-deposition residue in the deposition chamber. For instance, in a deposition chamber in which oxides or nitrides of titanium have been deposited, residual titanium compounds react with chlorine- or fluorine-containing gaseous cleaning agents to produce chlorides and fluorides of titanium. These byproducts from the reaction of the gaseous cleaning agents and the post-deposition residue also become incorporated into the material layers.
These halogen-containing compounds affect the rate at which the material layer is deposited, raise the dielectric constant of the material layer, cause embrittlement of the material layer, and corrode or degrade exposed capacitor and contact structures. For instance, if fluorine is present in the deposition chamber, it is known to decrease the rate of atomic layer deposition (ALD) of silicon oxide from tris-tertbutylsilanol (TBOS). The halogen-containing compounds in the deposition chamber also raise the cost of the semiconductor devices by increasing the fabrication time needed to form a semiconductor device that meets performance quality and lifetime specifications. Therefore, reducing or eliminating the halogen-containing compounds remaining after conventional cleaning processes is of significance to the cost-effective fabrication of semiconductor devices that have high-quality performance and long performance life.
One technique of removing the halogen-containing compounds from the deposition chamber is to purge the deposition chamber with an inert gas or combination of inert gases. For instance, argon and nitrogen are commonly used to purge deposition chambers in which NF3 cleaning has taken place. Long purge times are necessary to remove the halogen-containing compounds from the inside of the deposition chamber. However, these lengthy purge times do not effectively remove halogen-containing compounds that are adsorbed to the surfaces of the deposition chamber. To remove these adsorbed halogen-containing compounds, multiple depositions on “dummy” or “conditioning” wafers are performed until the halogen contamination has been reduced to an acceptable level. Oftentimes, as many as twenty dummy wafers are used before the halogen contamination has reached an acceptable level. Running the dummy wafers adds additional processing steps to the fabrication of the semiconductor devices, which reduces the number of semiconductor devices that is fabricated in a given time period, raises the costs of the semiconductor devices, and reduces profits realized by manufacturers.